This project addresses the need for the development of field deployable, sensors which provide real- time quantitative measurements at point-of-contact of airborne species that are injurious to human health - in this particular case, nitrogen dioxide and light-absorbing carbon. Nitrogen dioxide (NO2) is a highly toxic gas which when inhaled, causes the formation of nitric acid in the lungs and is thought to trigger asthmatic attacks. Light absorbing carbon (or LAC, a classification which includes soot, black carbon, brown carbon, graphitic carbon, etc.) comprises a significant fraction of respirable particles. Both species are byproducts of combustion systems including motor vehicles (especially diesel-powered), power plants, incinerators and other stationary combustors. Numerous epidemiological studies have shown that long-term exposure to fine particles and/or gases such as nitrogen dioxide produced by vehicular traffic is associated with various forms of heart and lung disease. The proposed program, a collaborative effort between Aerodyne Research, Inc. (a small business) and the Harvard School of Public Health, will involve the design, construction, verification and field testing of portable sensors which will provide real time data output which can be collected using a WiFi network. The sensors are based on a state-of-the-art optical technique, called cavity attenuated phase shift spectroscopy (CAPS), which utilizes very high reflectivity (R>0.9998) mirrors in an optical cavity in order to provide the long path length ((hundreds of meters) required to detect these species optically. Instead of employing a Beer's Law measurement, in which the intensity of light is measured, these monitors measure the average photon lifetime within the cavity, a quantity which is directly related to the concentration of the absorbing species. As such, they provide higher sensitivity, stability and reliability than instruments that employ more conventional techniques. The sensors to be developed will provide fast time response (<30 seconds) and high sensitivity (1 ppbv for nitrogen dioxide and 1 5g m-3 for LAC);real-time data streaming to the internet via a Wi-Fi connection will be included in the sensor unit. The sensors will operate for periods of 8 hours or longer using batteries and will be comparable in weight to a lightweight laptop computer. PUBLIC HEALTH RELEVANCE: These monitors will be used by the air pollution research community to monitor point-of- contact exposure to nitrogen dioxide and light-absorbing carbon. They can also be deployed in factories, power plants, incinerators and other stationary combustor facilities that are subject to occupational health and safety regulations.